Neural organization and neural interactions in mammalian retinas are investigated using intracellular electrophysiology, electron microscopy, and pharmacology. A hyperpolarizing amacrine cell, identified as type A8, has been penetrated with a sharp microelectrode, studied electrophysiologically, injected with HRP, and observed in the electron microscope. Cone dominated physiology, and predominant connections with hyperpolarizing cone bipolar cells in the inner plexiform layer were observed. Suppressive rod-cone interaction (SRCI) is a lateral interaction whereby dark-adapted rods antagonize cone signals. GABAergic effects on SRCI have been investigated in horizontal and ganglion cells in cat retina. Bicuculline and picrotoxin had no effects on SRCI in horizontal cells, but appeared to block the effect at the ganglion cell level by increasing dark-adapted, but not light-adapted, cone-signal amplitudes. Thus, SRCI may originate at multiple sites in the retina with different sensitivities to GABAA antagonists. In lower vertebrates, dopamine reduces receptive field size of retinal horizontal cells through metabotropic uncoupling of inter-horizontal-cell gap junctions. The effects on mammalian retina were studied. Horizontal cell receptive fields in cat and rabbit retinas were little influenced by dopaminergic ligands (dopamine, apomorphine, SKF38393, SCH23390, sulpiride) in the 70-700 micromole range. Small observed changes (+/-20% in space constant) appear near the limit of measurable repeatability. Results suggest that dopamine is not a major modulator of receptive fields in mammalian horizontal cells. Voltage noise in cat ON-beta ganglion cells increases during photic stimulation. Such noise may provide insight into the nature of synaptic transmission between bipolar and ganglion cells. Two types of events were identified: large (about 1 mV) monophasic depolarizing signals which may reflect action potentials leaked through gap junctions from adjacent ON-beta cells, and a smaller Gaussian distributed noise. Analysis of the latter suggests a quantal size of about 12 mu V and a release rate of about 100 quanta per second per bipolar-to-beta-cell synapse.